Ultraviolet luminescent retroreflective sheeting

ABSTRACT

Ultraviolet luminescent retroreflective sheeting includes a retroreflective portion containing retroreflective elements and an ultraviolet luminescent portion to facilitate nighttime viewing by persons not located at or near a source of light being retroreflected by the retroreflective portion. At least part of the ultraviolet luminescent portion is provided as the bonding lines for bonding the transparent cover sheet to the support sheet to form a series of sealed cells in which the retroreflective elements, which may be of the encapsulated lens-type or the encapsulated cube-corner-type, are disposed. The ultraviolet luminescenct portion includes fluorescent agent which emits light when irradiation by ultraviolet irradiation. The ultraviolet luminescent retroreflective sheeting may be used in a display device, such as a roadside sign, in combination with a source of ultraviolet radiation means which may be formed integrally with the sheeting or spaced therefrom and which will, in operation, emit ultraviolet rays in the direction of the retroreflective sheeting.

TECHNICAL FIELD

This invention relates to a retroreflective sheeting which is useful formarkings such as road signs, directional signs and construction signs;number plates on vehicles such as automobiles and motorcycles; safetygoods such as safety cloths and survival equipment; and markingmaterials for signboards, vehicles, etc. More particularly, theinvention relates to an ultraviolet luminescent retroreflective sheetingcomposed of a retroreflective region in which retroreflective elementsare disposed and an ultraviolet luminescent region which emits lightunder ultraviolet radiation, said ultraviolet luminescent regioncontaining a fluorescent agent which emits light under ultravioletradiation and a resin component, and the luminance of said light beingwithin a specific range.

Background Technology

Retroreflective sheetings which retroreflex light towards the lightsource are well known. Utilizing their excellent visibility at night dueto the retroreflective property, the sheetings have been used in wideareas as above. For example, road signs, construction signs or the likeusing a retroreflective sheeting reflex light from a light source suchas headlight of a running vehicle like automobile in the direction ofthe light source at night, i.e., in the direction of the runningautomobile, to provide excellent visibility to the driver of the vehiclewho sees the sign. Thus the sheeting exhibits a very favorable propertyof whereby enabling transmission of accurate informations.

Whereas, since retroreflective sheetings in general reflex-reflect lightfrom a light source toward the light source, they offer excellentvisibility in the direction of the light source, but only markedlyinferior visibility to the persons who are not in the direction of thelight source. Furthermore, because of the property innate inretroreflective sheeting, as a light source on a vehicle like anautomobile approaches a retroreflective sheeting-made sign, thedivergence between the angle of incident light from the light source andthat of the driver's observation increases, to substantially reduce thevisibility. Besides, accompanying recent road system development anddiversification in informations to be transmitted, amount ofinformations loaded on single directional sign is increasing, and whenspeed of a running vehicle is taken into consideration, it has becomevery difficult for a driver to read the necessary informations within anextremely short time during which he stays in the area wherefrom theretroreflective light is visible.

For those reasons, conventional type retroreflective sheetings havingthe retroreflective ability alone provide only insufficient visibilitywhen they are put to the usages where more accurate information supplyor higher advertising effect are required. In particular, high qualityretroreflective sheeting, which is capable of offering always excellentvisibility, even at night, for example, and even to persons who arelocated in the directions differing from that of the light source, hasbeen strongly demanded.

Aiming at meeting this demand, various attempts have been made toimprove visibility of retroreflective sheeting. For instance,JP-A-173008/1993 discloses an encapsulated lens-type retroreflectivesheeting exhibiting, concurrently with retroreflectivity, longpersistent phosphorescence, in which a transparent resin layer is usedas a support layer and a layer of long persistent phosphorescentsubstance is provided on the back of the support layer (the surfaceopposite to the incident side). However, the luminous energy of theluminescent substance is low and besides, visibility-improving effect ofthis proposal is yet definitely insufficient, because according to theproposal the layer of long persistent phosphorescent substance is underthat of the microspherical lens layer and, of the light emitted by thesubstance, mainly only the part which transmitted the spaces between themicrospherical lenses is visible.

PCT International Publication WO 93/14422 discloses a photoluminescentencapsulated cube-corner type retroreflective sheeting in which thebonding portion connecting the surface on the cube-corner-forming sideand the support layer contains phosphorescent pigment. The internationalpublication also suggests a method for imparting photoluminescence tosealed lens-type retroreflective sheeting and encapsulated lens-typeretroreflective sheeting. In this second proposal also, however, theluminous energy emitted from the phosphorescent pigment is not high,similar to that of the long persistent phosphorescent substance employedin the first proposal, and cannot provide high visibility allowingperception of information contained therein, when the sheeting is usedfor signs, from places apart from the signs at a substantial distance.

Furthermore, for example JP-A-43819/1994 proposes to improve visibilityby combining fluorescent coloring agent with retroreflective sheeting,but conventional fluorescent coloring agents generally exhibit poorweatherability and are inadequate for usages requiring long-termweatherability, such as for road signs. Again, the luminescent intensityis yet insufficient, and the visibility-improving effect achievable withthe proposal is not satisfactory.

For improving visibility in general, internally lighted signboards,electric signboards, externally lighted signboards or the like are used,but for signs of elevated set up like road signs or directional signs,internally lighted or electric signboards are difficult of maintenance.There is still another drawback that signs of these systems are largescaled and expensive. In addition, internally lighted signboards havebeen subject to the problems that borderlines between different colorsare blurred or characters are defaced, rendering it difficult toaccurately express the content to be conveyed.

Also in electric signboards, the light-emitting elements are large andindependent of each other. In consequence, unevenness in the luminescentplane is apt to occur due to differences in life span of said elements.Besides, they are subject to a problem because they adopt line- ordot-luminescent system, that they cannot precisely express thecharacters or designs to be displayed. Externally lighted signboardshave an advantage that they exhibit excellent visibility to persons whoare in the directions other than that of the light source as well, buton the other hand have such inconveniences when they are used as trafficdirectional signs containing a large volume of informations that cardrivers have difficulties in perceiving their contents from distantplaces due to insufficient luminous energy or the like and hence thedrivers are required to instantaneously comprehend the whole contents asthey sufficiently approach the signs.

We have conducted various investigations on visibility ofretroreflective sheeting and discovered: a superb retroreflectivesheeting exhibiting excellent visibility to not only those who are inthe light source direction but also those who are in the directionsother than the light source direction is obtained by forming anultraviolet (UV) luminescent region on a part of a retroreflectivesheeting, with a UV luminescent resin composition comprising afluorescent agent which emits light under UV rays (which may behereafter referred to briefly as "UV fluorescent agent") and a resincomponent; and when said retroreflective sheeting is used in combinationwith a UV radiation means which radiates UV in the direction of saidretroreflective sheeting as used in, for example, display devices suchas road signs or directional signs, drivers of vehicles like automobilescan recognize contents of the signs by the reflex-reflection when theyare distant from the display devices, and by the UV luminescence as theyapproach the devices. The present invention is thus completed.

Disclosures of the Invention

Thus, according to the present invention an ultraviolet luminescentretroreflective sheeting composed of a retroreflective region in whichretroreflective elements are disposed and an ultraviolet luminescentregion which emits light under ultraviolet radiation is provided, saidsheeting being characterized in that said ultraviolet luminescent regioncontains a fluorescent agent which emits light under ultraviolet raysand a resin component, and the luminance of the ultraviolet luminescentregion, when irradiated with a fluorescent lamp which emitsnear-ultraviolet rays of main wavelength around 360 nm at alight-receiving intensity of 0.8 mW/cm², is at least 10 cd/m².

Again, according to the present invention as above, a display devicewhich comprises, in combination, an ultraviolet luminescentretroreflective sheeting and a means for radiating ultraviolet rays inthe direction of said retroreflective sheeting, is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of schematic plan view of a UV luminescentretroreflective sheeting of the present invention having encapsulatedlens-structured retroreflective region, as seen from the incident side.

FIG. 2 is a schematic cross-sectional view of the retroreflectivesheeting of FIG. 1, cut along A--A in FIG. 1.

FIG. 3 is another example of a schematic plan view of a UV luminescentretroreflective sheeting of an embodiment of the present inventiondiffering from that of FIG. 1, having encapsulated lens-structuredretroreflective region, as seen from the incident side.

FIG. 4 is a schematic cross-sectional view cut along B--B in FIG. 3.

FIG. 5 is a schematic cross-sectional view illustrating an example of UVluminescent retroreflective sheeting of the present invention havingsealed lens-structured retroreflective region.

FIG. 6 shows an example of UV luminescent retroreflective sheeting ofthe present invention having encapsulated cube corner-structuredretroreflective region.

FIG. 7 shows another example of UV luminescent retroreflective sheetingof the present invention having encapsulated cube corner-structuredretroreflective region, which is an embodiment different from that ofFIG. 6.

FIG. 8 shows a display device according to the present invention inwhich a UV luminescent retroreflective sheeting of the present inventionis integrally combined with a UV luminescent lamp as a UV radiationmeans.

Hereafter the ultraviolet luminescent retroreflective sheeting of thepresent invention shall be explained in further details, referring toFIGS. 1-8.

In a UV luminescent retroreflective sheeting of the present invention,the retroreflective element which is a constituent of theretroreflective region is not subject to any critical limitations. Theelement may be, for example, a lens-type retroreflective element formedof microspherical lenses such as glass beads and a photo-reflectivemetallized layer, cube-corner type retroreflective element wherein eachpair of confronting planes face with each other at an angle ofapproximately 90°, or the like.

Again the construction of the retroreflective region is subject to nospecific limitation. For example, it may be exposed lens-type,encapsulated lens-type, sealed lens-type, encapsulated cube corner-typeor metal vapor-coated cube corner-type retroreflective structure.

An exposed lens-type retroreflective structure comprises a support layerand many microspherical lenses which are disposed forming substantiallyin a monolayer and are embedded in the incident side surface of saidsupport layer to about their hemispheres which are covered with aphoto-reflective metallized layer.

An encapsulated lens-type retroreflective structure is illustrated, forexample, by the schematic cross-sectioned views of FIGS. 2 and 4, inwhich the retroreflective region is composed of a light-transmittingcover layer; support layer; a layer of lens-type retroreflectiveelements which are many microspherical lenses disposed on the surfacefacing the light-transmitting cover layer of the support layer assubstantially a monolayer, and supported by the support layer as theyare embedded in said layer to their hemispheres, said embeddedhemispheres being covered with photo-reflective metallized membrane; andan air layer between the light-transmitting cover layer and the layer oflens-type retroreflective elements, said air layer being formed as thelight-transmitting cover layer and the support layer are partiallyconnected by bonds while leaving spaces between said two layers at theparts where said two layers are not connected by bonds, and said bondsdividing said air layer into a large number of hermetically sealed smallcompartment cells.

Sealed lens-type retroreflective structure can be illustrated, forexample, by the schematic cross-sectional view of FIG. 5, in which theretroreflective region is composed of a light-transmitting supportlayer; a layer of microspherical lenses which are disposed formingsubstantially a monolayer on the surface of the light-transmittingsupport layer opposite to its incident side surface and are supported bysaid support layer as embedded therein to about their hemispheres; alight-transmitting focusing layer formed approximately along thesurfaces of their hemispheres unembedded in the support layer of themicrospherical lenses and having such a thickness that places thesubstantial foci for the microspherical lenses on the surface of theside not coming into contact with said lenses; and a photoreflectivemetallized membrane which is formed on the surface of the focusing layernot coming into contact with the microspherical lenses. Also as shown inFIG. 5, if necessary an additional light-transmitting surface-protectivelayer may be laminated on the incident surface of the support layer.

Examples of encapsulated cube-corner type retroreflective structure areillustrated by the schematic cross-sectional views of FIGS. 6 and 7,which are composed of a light-transmitting cover layer; a layer ofcube-corner type retroreflective elements which is disposed on the backof said cover layer; a support layer; and an air layer between saidcube-corner type retroreflective element layer and the support layer;said air layer being formed as the cube-corner type retroreflectiveelement layer and the support layer are partially connected by bondswhile leaving spaces between said two layers at the parts where said twolayers are not connected by bonds, and said bonds dividing the air layerinto a large number of hermetically sealed small compartment cells. Alsoas shown in FIG. 7, if necessary an additional light-transmittingsurface-protective layer may be laminated on the incident surface of thelight-transmitting cover layer.

A metal vapor-coated cube-corner type retroreflective structure refersto one which comprises at least a light-transmitting cover layer; alayer of cube-corner type retroreflective elements which is disposed onthe back of said cover layer; and a photo-reflective metallized membranewhich is formed on the entire surface of the cube-corner typeretroreflective elements. Again if necessary an additionallight-transmitting surface-protective layer may be laminated on theincident surface of the light-transmitting cover layer.

The support layer to be used in the UV luminescent retroreflectivesheeting of the present invention may be formed of same resins which areuseful as the resin component of UV luminescent resin compositions,e.g., acrylic resins, urethane resins, polyester resins, vinyl chlorideresins, vinyl acetate resins, polyolefin resins, fluorine-containingresins, polyamide resins, etc., which can be used either singly or incopolymerized form with other(s) of such resins, or in blended form.

Said support layer may be crosslinked by the action of a crosslinkingagent such as of isocyanate-, melamine- or metal-type, and if necessarymay contain various fillers such as cellulose derivatives, multistagepolymerization type internal crosslinked resins, coloring agents, UVfluorescent agent, light storing color developers, heat stabilizers,ultraviolet absorbers, etc. Preferred thickness of the support layernormally ranges approximately 20-200 μm.

For lens-type retroreflective structure, the support layer is notnecessarily composed of a single layer, but may be composed of a binderlayer supporting the glass beads as embedded therein and a reinforcinglayer which is laminated on the surface of the binder layer opposite tothe glass beads-embedded side. The thickness of the reinforcing layer isconveniently designed normally to be within a range of 10-100 μm, inparticular, 30-80 μm. The support layer may further include anintermediate layer between the binder layer and the reinforcing layer,for increasing adhesive power of said two layers.

A light-transmitting cover layer useful for the UV luminescentretroreflective sheeting of the present invention and alight-transmitting surface-protective layer optionally laminated ifnecessary have a total light transmittance of at least 20%, preferablyat least 40%, and exhibit a reasonable extent of pliability. Otherwise,they are not particularly limited as to their material which may be, forexample, acrylic resin film, fluorine-containing resin film,polyurethane resin film, vinyl chloride resin film, polycarbonate resinfilm, polyester resin film, polyolefin resin film or the like.

It is normally preferred that these cover layer and surface-protectivelayer are unstretched, because monoaxially or multi-axially stretchedfilm is apt to be subject to residual strain which impairs durability ofthe produced retroreflective sheeting, while the stretching increasesmechanical strength of the film. The thickness of the cover layer isvariable over a wide range depending on the intended use of theretroreflective sheeting as the final product, while it normally ranges20-200 μm, preferably 40-150 μm, inter alia, 50-100 μm. The thickness ofthe surface-protective layer is normally set to be 10-200 μm, preferably20-150 μm, inter alia, 30-100 μm.

Retroreflective sheetings having above-described various retroreflectivestructures and their production processes are described in a number ofpublications: for example, exposed-lens type retroreflective sheeting isdisclosed in U.S. Pat. No. 2,326,634, JP-A-189839/1982; encapsulatedlens-type retroreflective sheeting, for example, in JP-A-194405/1985(corres. to U.S. Pat. No. 4,653,854); sealed lens-type retroreflectivesheeting, for example, in JP-B-2921/1981 (corres. to U.S. Pat. No.4,025,674); encapsulated cube-corner type retroreflective sheeting, forexample, in U.S. Pat. No. 3,417,959; and vapor coated metal cube-cornertype retroreflective sheeting, for example, in JP-A-106839/1974 (corres.to U.S. Pat. No. 3,712,706), etc. These references are cited hereinstead of describing those products and processes more specifically.

The UV luminescent retroreflective sheeting of the present invention hasthe prominent characteristic feature in that it contains, concurrentlywith the above-described retroreflective region, a UV luminescent regionemitting light under UV radiation. The retroreflective region hasretroreflectability, and functions to reflex-reflect light from a lightsource toward the light source direction to offer excellent visibilityto those who are in said direction. Whereas, the UV luminescent regionemits light, under UV radiation from a UV radiating means such as a UVlamp or the like, to diverse directions so as to provide excellentvisibility to those who are in the locations not in the direction of thelight source as well.

In a UV luminescent retroreflective sheeting of the present invention,said UV luminescent region preferably contains a resin componentconcurrently with a fluorescent agent which emits light under UV rays.When said region is irradiated with near-ultraviolet rays of the mainwavelength around 360 nm from a fluorescent lamp at a light receivingintensity of 0.8 mW/cm², the region is required to have a luminance ofat least 10 cd/m², preferably at least 15 cd/m², inter alia, at least 20cd/m². When the luminance is less than the above lower limit, the regioncannot provide sufficient visibility.

The luminance of the light emitted from the UV luminescent region ismeasured according to the later described method.

The UV luminescent region according to the present invention is formedof a UV luminescent resin composition containing, per 100 parts byweight of the resin component, preferably 10-600 parts by weight, inparticular, 50-400 parts by weight, inter alia, 100-300 parts by weight,of a UV fluorescent agent. When the added amount of UV fluorescent agentis at least the above-specified lower limit, satisfactory luminescentfunction and excellent visibility can be obtained. Again, when theamount is not more than the above upper limit, such an inconveniencethat the formed UV luminescent region becomes too hard and brittle isavoided and desirable properties such as mechanical strength,pliability, etc. are not impaired. Thus, the range as above specifiedgives favorable result.

Said UV fluorescent agent signifies any fluorescent agents which emitlight under UV radiation. As long as they are capable of forming a UVluminescent region satisfying aforesaid luminance requirement, they aresubject to no other particular limitations, but can be optionallyselected from various fluorescent agents, e.g., organic fluorescentagents which generally exhibit relatively high photo-transmittance suchas naphthotriazoles and benzoxazoles; and generallynon-photo-transmitting inorganic fluorescent agents such as inorganicmetal salts, halides and sulfides, etc.

Examples of the organic fluorescent agents include, besidesdiaminostylbenzene, uranine, thioflavine T, eosine, Rhodamine B andAcridine Orange, organic pigments derived from diphenylmethane,triphenylmethane, xanthene, thiazine and thiazole dyes. These can beused either singly or as mixtures of more than one materials.

Examples of the inorganic fluorescent agent include green light-emittinginorganic fluorescent agents such as Zn₂ GeO₄ :Mn, ZnO:Zn, ZnS:Cu,ZnS:(Cu,Al), (Zn,Cd)S:(Cu,Al), ZnS:(Cu,Au,Al), Zn₂ SiO₄ :Mn,ZnS:(Cu,Ag), (Zn,Cd)S:Cu, Gd₂ O₂ S:Tb, La₂ O₂ S:Tb, Y₂ SiO₅ :(Ce,Tb),CeMgAl₁₁ O₁₉ :Tb, ZnS:(Cu,Co), LaOBr:(Tb,Tm), La₂ O₂ S:Tb, BaMg₂ Al₁₆O₂₇ :(Eu,Mu), etc.; red light-emitting fluorescent agents such as; Y₂ O₃:Eu, Y(P,V)O₄ :Eu, Y₂ O₂ S:Eu 0.5MgF₂.3.5MgO.GeO₂ :Mn, YVO₄ :Eu,(Y,Gd)BO₃ :Eu, etc.; blue light-emitting fluorescent agents such as; Sr₅(PO₄)₃ Cl:Eu, BaMg₂ Al₁₆ O₂₇ :Eu, BaMgAl₁₀ O₁₇ :Eu, ZnS:Ag, CaWO₄, Y₂SiO₅ :Ce, ZnS:(Ag,Ga,Cl), Sr₂ P₂ O₇ :Eu, CaS:Bi, CaSrS:Bi, etc. They canbe used either singly or as mixtures. It is also permissible to usethese inorganic fluorescent agents in combination with above organicfluorescent agents.

Inorganic fluorescent agents generally excel over organic fluorescentagents in photostability, heat stability, solvent resistance, etc. anduse of those inorganic agents is preferred depending on the environmentsin which the UV luminescent retroreflective sheeting is to be used. Ofthose inorganic agents, furthermore, in particular above-named green,red or blue light-emitting inorganic fluorescent agents are preferred,because of the advantage that their UV luminescent luminance is high andgives excellent visibility at night.

Again, of those inorganic fluorescent agents, those having a particlesize distribution that at least 80% by weight of the particles have asize 25 μm or less in diameter are preferred. As for those greenlight-emitting inorganic fluorescent agents, those having a particlesize distribution width of 0.1-50 μm and the highest frequency particlesize of approximately 12 μm are preferred; for the red light-emittingagents, those having a particle size distribution width of 0.1-8 μm andthe highest frequency particle size of approximately 3 μm; and for theblue light-emitting agents, those having a particle size distributionwidth of 0.1-12 μm and the highest frequency particle size of 8 μm; areconveniently used.

Furthermore, as these inorganic fluorescent agents, generally thosewhich emit light under radiation of UV rays of wavelengths ranging250-400 nm are preferred.

The resin component to be contained in the UV luminescent resincomposition forming the UV luminescent region, concurrently withabove-explained UV fluorescent agent, is not subject to any specificlimitation as to the kind of the resin, so long as the resin can retainthe UV fluorescent agent as dispersed therein. Examples of useful resinsinclude acrylic resins, urethane resins, polyester resins,fluorine-containing resins, vinyl chloride resins, vinyl acetate resins,polyethylene resins, polypropylene resins, polycarbonate resins, etc.which can be used either singly or as copolymerized or blended. Ofthese, acrylic resins, urethane resins,. polyester resins andfluorine-containing resins are preferred because of their goodweatherability and processability, acrylic resins being the mostconvenient.

The UV luminescent resin composition may further contain, besides theresin component and UV fluorescent agent, a coloring agent such asordinary colorant, long persistent phosphorescent color developer, etc.and other additives such as photostabilizer, heat stabilizer, filler,crosslinking agent, etc., as individual occasion demands.

In the construction of the UV luminescent retroreflective sheeting ofthe present invention, the manner of disposition of UV luminescentregion forming a part of said sheeting is not critical. The region maybe formed in each desired location(s) in desired configuration. Forexample, a retroreflective region and a UV luminescent region may beseparately and locally disposed, or either one of the regions may beprovided over the entire area and the other region can be disposedthereover or thereunder, either partially or wholly. Furthermore, it isalso possible to provide a UV luminescent region at an intermediatelayer position of a multilayer-structured retroreflective region such asof aforesaid sealed lens-type retroreflective structure or capsule typeretroreflective structure, for example, below the light-transmittingcover layer or light-transmitting surface-protective layer, eitherpartially or wholly.

Whereas, when a non-light-transmitting UV luminescent region is formedor disposed above the retroreflective elements in the retroreflectiveregion, using a UV luminescent resin composition containing a normallynon-light-transmitting fluorescent agent such as an inorganicfluorescent agent, it should be avoided to provide the UV luminescentregion over the entire retroreflective region, because theretroreflective performance of the retroreflective elements under such aUV luminescent region is impaired. Similarly, when anon-light-transmitting retroreflective region or non-light-transmittingportion of a retroreflective region is disposed above a UV luminescentregion, it is necessary to avoid providing the former over the entire UVluminescent region, because the UV luminescent performance of the UVluminescent region underneath is impaired.

When a light-transmitting or semi-light-transmitting UV luminescentregion or a retroreflective region is used, it is possible to placeeither one of the regions over the entire surface of the other. In thatcase, a UV luminescent retroreflective sheeting is provided in which anidentical part has both UV luminescent property and retroreflectiveproperty.

In those various embodiments of the UV luminescent retroreflectivesheeting of the present invention, when the intended use of the sheetingis for durable display devices such as road signs or directional signs,it is preferred to form the UV luminescent region using a UV luminescentresin composition containing an inorganic fluorescent agent whichgenerally exhibits better photostability, heat stability, solventresistance, etc. compared with organic fluorescent agent as statedearlier. Whereas, because inorganic fluorescent agents are normallynon-light-transmitting, a UV luminescent region containing an inorganicfluorescent agent cannot be provided over the entire upper surface of aretroreflective region and when it is used in combination with aretroreflective region having lens-type retroreflective elements of anexposed, encapsulated or sealed structure, it should be formed partiallyover such a retroreflective region. It is also possible to form a UVluminescent layer with this type of UV luminescent resin composition onthe upper surface of an ordinary support layer and thereafter to embedglass beads therein in a monolayer level, so as to let the spacesbetween the glass beads serve as a UV luminescent region. Furthermore,these means can be employed in combination.

Of these retroreflective regions, when one having an encapsulatedlens-type or sealed lens-type retroreflective structure is to becombined with a UV luminescent region, the luminescent region ispreferably formed under the light-transmitting cover layer of theretroreflective structure, for better durability or pollution resistanceof the UV luminescent region. In particular, when the retroreflectiveregion has an encapsulated lens-type retroreflective structure, it ispreferable to make the bonds partially connecting said cover layer withthe support layer holding said lens-type retroreflective elements serveas the UV luminescent region, and if necessary to further provide a UVluminescent layer on a part of the capsule-facing side of the coverlayer or to let the spaces between the glass beads also serve as the UVluminescent region as stated earlier, or to combine these means. Again,in combining with a sealed lens-type retroreflective structure, it ispreferred to form the UV luminescent region on the incident side surfaceof the support layer, i.e., the side opposite to the microsphericallenses-embedding surface, and/or on the support layer-facing side of thesurface-protective layer which is laminated on the incident side of saidsupport layer, to sandwich the UV luminescent region between thesurface-protective layer and the support layer.

Furthermore, when combined with a retroreflective region having anencapsulated cube-corner type structure, preferably the UV luminescentregion is formed under the light-transmitting cover layer, and/or, ifnecessary, under the light-transmitting surface-protective layer whichis laminated on the incident side surface of the cover layer, for thesame reason as stated above. More specifically, a part or whole of thebonds connecting the light-transmitting cover layer with the supportlayer can be made the UV luminescent region; or the UV luminescentregion may be formed on the incident-side surface of the cover layer,i.e., the surface on which cube corners are not formed, and/or the coverlayer-facing side of the surface-protective layer which is laminated onthe incident-side surface of the cover layer. Because cube-corner typeretroreflective elements are formed on the back of thelight-transmitting cover layer and are themselves transparent, the UVluminescent region may be formed on the support layer, over the whole ofsaid layer or part of optionally determined area.

When combined with a retroreflective region of a metal vapor-coatedcube-corner type, the UV luminescent region can be formed on theincident-side surface of the cover layer, i.e., the surface on which thecube corners are not formed, and/or the cover layer-facing side of thesurface protective layer which is laminated on the incident-side surfaceof the cover layer.

The means for forming a UV luminescent layer according to the presentinvention is not critical per se. For example, printing means such asscreen print, photogravure using the earlier described UV luminescentresin compositions is preferred, because it allows relatively easyformation of the regions of even complicated pattern. In particular,screen printing is the most convenient, which can form a thick layer bysingle operation.

Again, in a preferred embodiment of a UV luminescent capsule-typeretroreflective sheeting according to the present invention, preferablythe bonds partially connecting the cover layer and the support layer areformed on either the cover layer or the support layer using the UVluminescent resin composition, as earlier described, as a UV luminescentlayer by said printing means, and then they are melt-bonded to eitherthe support layer or cover layer under heating, or adhered by a suitableadhesive. Furthermore, the support layer may be formed of the UVluminescent resin composition, or a UV luminescent layer may be formedon an ordinary support layer with said resin composition, and such asupport layer or a laminate of the support layer and a UV luminescentlayer is partially thermofused and formed into the bonds which partiallyconnect the cover layer and support layer, with such means as anembossing roll.

In the UV luminescent retroreflective sheeting of the present inventionwhere its UV luminescent region uses a non-light-transmitting inorganicfluorescent agent, generally the areal ratio of the retroreflectiveregion can be within a range of 10-90%; that of the UV luminescentregion, within a range of 10-100%; and the sum of the areal ratios ofthe two regions is suitably designed to be at least 85%; when the totalarea of the incident-side surface of the sheeting is set to be 100%.Preferably, the areal ratios of these two regions should be determineddepending on the kind of the retroreflective elements used. When theretroreflective region is of lens-type, the areal ratio of theretroreflective region may range 10-70%, in particular, 20-60%, interalia, 30-50%; that of the UV luminescent region may range 10-90%, inparticular, 30-80%, inter alia, 40-70%; and the sum of the areal ratiosof the two regions may range 90-120%, in particular, 100%.

When the retroreflective region is of cube-corner type, those arealratios are preferably designed to make that of the retroreflectiveregion 10-90%, in particular, 15-80%, inter alia, 20-60%; that of the UVluminescent region, 10-100%, in particular, 20-85%, inter alia, 40-80%;and the sum of the areal ratios of the two regions, 90-190%, inparticular, 90-120%, inter alia, 100%.

In the above, the area of a retroreflective region refers to the area ofthe part actually having retroreflective ability. For example, in anencapsulated lens-type retroreflective region, said area corresponds tothe value obtained by subtracting, from the total area of theincident-side surface, those of the parts which are closer to saidsurface than the retroreflective region is, i.e., subtracting the areaswhose retroreflectivity is lost, such as the area ofnon-light-transmitting UV luminescent region which is formed on thelight-transmitting cover layer or light-transmitting surface-protectivelayer or directly on the retroreflective region by means of printing,etc., and those of the bonds which are formed by partial thermofusingand thermoforming of the support layer.

In case of a sealed lens-type retroreflective region, the area is oneobtained by subtracting, from the total area of the incident-sidesurface, those of the parts which are closer to said surface than theretroreflective region is, i.e., subtracting the area of the part whoseretroreflectivity is lost, such as the area of non-light-transmitting UVluminescent region formed on the light-transmitting cover layer orlight-transmitting surface-protective layer surface, by such means asprinting, etc.

When the retroreflective elements are of encapsulated cube-corner type,the retroreflective area is the value obtained by subtracting, from thetotal area of the incident-side surface, those of the parts closer tosaid surface than the retroreflective region is, i.e., subtracting theareas of the parts whose retroreflectivity is lost, such as thenon-light-transmitting UV luminescent region which is formed on thelight-transmitting cover layer or light-transmitting surface-protectivelayer surface by such means as printing, etc., and the bonds which areformed by printing, etc. or by partial thermofusing and thermoforming ofthe support layer.

Hereinafter the UV luminescent retroreflective sheeting of the presentinvention is more specifically explained with reference to the preferredembodiments as illustrated in FIGS. 1-8.

FIG. 1 is an example of schematic plan view of a UV luminescentretroreflective sheeting of the present invention having encapsulatedlens-structured retroreflective region, as seen from the incident side,in which: (5) is a UV luminescent layer forming a UV luminescent regions(7); (8) are hermetically sealed, small compartment cells (capsules)containing retroreflective elements, and form a retroreflective region(6).

FIG. 2 is a schematic cross-sectional view of the retroreflectivesheeting of FIG. 1, cut along A--A in FIG. 1. In FIG. 2, (1) is alight-transmitting cover layer, and (9) is a support layer in whichglass beads (3) are embedded to about their lower hemispheres; (10) arethe bonds connecting said light-transmitting cover layer (1) and supportlayer (9), the capsules (8) being formed upon disposition of thesebonds. The lower hemispheres of the glass beads (3) are covered with avapor-coated metal membrane (4) which serves as the photoreflective filmand functions as the retroreflective elements which retroreflex lighttoward the direction of light source. The bonds (10) are formed as a UVluminescent layer (5) of a UV luminescent resin composition by aprinting means such as screen printing and function as the UVluminescent region (7); and the glass beads (3)-embedded portion of thesupport layer which is not occupied by the bonds (10) is theretroreflective region.

FIG. 3 is a schematic plan view of a UV luminescent retroreflectivesheeting of the present invention having encapsulated lens-structuredretroreflective region, showing an embodiment differing from that ofFIG. 1, as seen from the incident side, in which: (5) is the UVluminescent layer forming UV luminescent regions (7); (8) are thecapsules containing retroreflective elements, the main portion thereofforming the retroreflective region (6).

FIG. 4 is a schematic cross-sectional view of the retroreflectivesheeting of FIG. 3, cut along B--B in FIG. 3. Similarly to FIG. 2, (1)is a light-transmitting cover layer and (9) is a support layer in whichglass beads (3) are embedded to about their lower hemispheres; (10) arethe bonds connecting said light-transmitting cover layer (1) and supportlayer (9), the capsules (8) being formed upon disposition of thesebonds. It is same to the embodiment of FIG. 2 that the lower hemispheresof glass beads (3) are covered with vapor-coated metal membrane (4) andserve as the retroreflective elements and that the bonds (10) are formedof a UV luminescent resin composition. Whereas, in this embodiment a UVluminescent layer (5) made of a UV luminescent resin composition isformed locally on the support layer-facing surface of thelight-transmitting cover layer (1), said bonds (10) and the UVluminescent layer (5) together form the UV luminescent region (7). Theparts of the support layer at which these bonds (10) and UV luminescentlayer (5) are not disposed and at which the glass beads (3) areembedded, function as the retroreflective region (6).

FIG. 5 is a schematic cross-sectional view illustrating an example of UVluminescent retroreflective sheeting of the present invention having asealed lens-structured retroreflective region. In FIG. 5, (11) is alight-transmitting surface-protective layer, and (2A) is alight-transmitting support layer supporting glass beads (3); (2B) is alight-transmitting focusing layer for forming a vapor-coated metalmembrane (4) serving as a photoreflective membrane, located atapproximately the focus spot of the lenses, said support layer (2A) andfocusing layer (2B) together forming a light-transmitting, sealing resinlayer (2) for sealing glass beads therein. The glass beads and thevapor-coated metal membrane function as retroreflective elements whichreflex the received light at the focussed spot of the lenses andretroreflex said light toward the light source. Underneath thelight-transmitting surface-protective layer (11) a UV luminescent layer(5) is formed, which functions as the UV luminescent region (7), and theparts of the lens-embedding surface above which said UV luminescentlayer (5) is not disposed function as the retroreflective region (6).

FIG. 6 shows an example of UV luminescent retroreflective sheeting ofthe present invention having encapsulated cube corner-structuredretroreflective region. In FIG. 6, (1) is the light-transmitting coverlayer, and (9) is the support layer, said cover layer being provided onits support layer (9)-facing surface with cube-corner type reflectiveelements in which each pair of confronting planes confront at an angleof about 90° are disposed and which function as the retroreflectiveelements to retroreflex light toward the direction of the light source;(10) are the parts connecting the light-transmitting cover layer (1) andthe support layer (9), provision of which resulting in formation ofcapsules (8). Said connecting parts (10) are formed of a UV luminescentresin composition and function as the UV luminescent region (7). Theretroreflective region (6) in this embodiment is the entire area of thelight-transmitting cover layer excepting the parts at which theconnecting parts (10) are adhered. By so providing UV luminescentregions (7) at the connecting parts (10), a UV luminescentretroreflective sheeting retaining the high retroreflectivity of thecube-corner type retroreflective sheeting is obtained.

FIG. 7 shows another example of UV luminescent retroreflective sheetingof the present invention having encapsulated cube corner-structuredretroreflective region, which is an embodiment different from that ofFIG. 6. Similar to the embodiment of FIG. 6, (1) is thelight-transmitting cover layer and (9) is the support layer, said coverlayer being provided on its support layer-facing surface with cubecorner-type reflective elements; (10) are the parts connecting thelight-transmitting cover layer (1) and the support layer (9), provisionof which resulting in formation of capsules (8). Again similar to theembodiment of FIG. 6, said connecting parts (10) are made of a UVluminescent resin composition and function as the UV luminescent region(7). Whereas, in this embodiment UV luminescent layer (5) is formed onthe incident side surface of the light-transmitting cover layer (1), tofunction also as the UV luminescent region (7). On the incident-sidesurface of the cover layer (1), a light-transmitting surface-protectivelayer (11) is formed. In this embodiment, therefore, the UV luminescentregion consists of the connecting parts (10) and the UV luminescentlayer (5) on the incident-side surface of the light-transmitting coverlayer (1), and the retroreflective region (6) is the area of thelight-transmitting cover layer (1) from which the parts bonded to theconnecting parts (10) and the parts covered by the UV luminescent layer(5) which is formed on said cover layer are excluded.

In FIGS. 2, 4, 6 and 7, the bonds (10) are primarily non-reflectiveparts in the retroreflective sheeting and do not contribute to theproduct's retroreflective performance. It is convenient to provide a UVluminescent region (7) at said bonds (10), to improve visibility atnight without adversely affecting the product's retroreflectiveperformance. It is also a preferred embodiment to form the bonds (10),which are UV luminescent regions, by partial thermofusing andthermoforming of a support layer containing UV fluorescent agent,because the embodiment provides highly intimate adhesion between thesupport layer and the light-transmitting cover layer. In these modes ofpractice, furthermore, the light-transmitting cover layer andlight-transmitting surface-protective layer are required to have theability to transmit UV of the wavelengths necessary for UV luminescence,so that they do not obstruct UV luminescence of the UV luminescentregions (7) which are provided under said layers.

The UV luminescent retroreflective sheeting of the present inventionexhibits superb function as a display device such as road signs oradvertisement sign boards, as combined with a UV radiation means whichirradiates UV in the direction of the retroreflective sheeting.

For example, as illustrated in FIG. 8, a display device according to thepresent invention, which is obtained by integrally combining a UVluminescent retroreflective sheeting of the present invention with a UVradiation means, such as a lamp which emits UV rays of the wavelengthsin the range of, for example, 250-400 nm, preferably 300-400 nm, is anexcellent display device exhibiting high visibility to persons locatedat various directions. In FIG. 8, (12) are the display part formed bysuitably cutting a UV luminescent retroreflective sheeting into suitablecharacters, figures or signs, etc., (14) is a UV radiating lamp and (13)is the background of the display part (12), which may be an ordinaryplate material such as a sheet steel painted in any desired color, orcan be a retroreflective sheeting colored differently from the color ofsaid display part or a UV luminescent retroreflective sheeting of thepresent invention emitting UV luminescence of different color tone. Inthe display device of the present invention, furthermore, it is notnecessarily required to integrally assemble the UV luminescentretroreflective sheeting and a UV radiation means. For example, when thedisplay part formed of the UV luminescent retroreflective sheeting ofthe display device is to be installed at a high place, a UV radiationmeans can be installed at a prescribed distance from the display part toradiate UV in the direction of the display part, whereby facilitatingmaintenance, e.g., replacement of the UV lamp which is the UV radiationmeans.

The display device of the present invention is capable of not onlyaccurately expressing the intended characters, design, etc. but alsoreadily providing a uniformly luminescent plane even over a wide area,differently from conventional internally lighted signboards or electricsignboards, because the UV luminescent elements in the UV luminescentretroreflective sheeting used therein are very small in size andfurthermore are regularly dispersed over the whole sheeting.Furthermore, by adequately selecting the kind of UV fluorescent agentused in the UV luminescent region, retroreflective sheeting emittingmulti-colored lights can be formed, whereby providing instantaneouslyexcellent visibility to the persons who are in the light sourcedirection as well as in the directions other than that of the lightsource. Still in addition, because UV fluorescent agent used in the UVluminescent region scarcely develops color under natural light,different designs can be expressed on an identical display plane ofsingle display device, under natural light and UV light, to diversifythe informations to be provided by the device.

EXAMPLES

Hereafter the present invention is explained more specifically by meansof working examples in which the retroreflectivity and UV luminance weremeasured as follows.

(1) Retroreflectivity

Using as the retroreflectivity-measuring instrument "Model 920" ofAdvanced Retro Technology Inc., amount (luminous energy) ofretroreflective light from retroreflective region of 100 mm×100 mm sizesample was measured following JIS Z-9117, at an observation angle of 12'and angle of incidence of 5', at optional five spots. The average of themeasured values is recorded as the retroreflectivity.

(2) UV luminance

Using a UV luminescent device having four 10W UV-emitting fluorescentlamps incorporated therein and a visible light-cutting filter providedon its front surface, which emitted near-ultraviolet rays whose mainwavelength was in the vicinity of 360 nm and wavelength range was300-420 nm, each 100 mm×100 mm size sample was irradiated from directlyoverhead with the receiving light intensity at the surface of the UVluminescent region being controlled to be 0.8 mW/cm². At a distance ofabout 30 cm in said direction, luminance at about 5 mmφ spot on the UVluminescent region surface was measured at optional 5 locations with aluminance meter "LS-100" Minoruta Camera K.K.!. The UV luminance A and Bwere determined as follows.

A: UV luminance of UV luminescent region (average of the five measuredvalues) (cd/m²)

B: Average UV luminance of UV luminescent retroreflective sheeting(cd/m²)

=A×areal ratio of UV luminescent region (% ÷100

(3) Visibility evaluation

A directional signboard was prepared by providing, on a 2200 mm×2700 mmaluminum plate, cut characters from a UV luminescent retroreflectivesheeting as the display part, using an encapsulated lens-typeretroreflective sheeting "Nikkalite ULS F806" (blue), Nikka PolymerK.K.! as the background. The signboard was installed high, at a distancefrom the ground to the lower edge of the signboard of about 4 m and in aposture that the sheet plane became approximately perpendicular. At aposition distant from the spot directly below the horizontal center ofthe signboard by about 5 m, a floodlight-type 400 W high-pressuremercury vapor lamp was installed and adjusted to radiate UV over theentire surface of the signboard.

At positions distant from the spot directly below the signboard by about100 m, twenty men and women monitors of 18-50 years old evaluatedvisibility of the signboard at night. The grading was conductedfollowing the scale below, and the average value was made the result ofthe visibility evaluation:

5: very clearly visible

4: normally visible

3: characters are difficultly visible

2: vaguely visible (characters are hardly discernible)

1: invisible.

Example 1

A provisional support composed of an about 20 μm-thick polyethylene (PE)layer as laminated on paper was heated to about 105° C., on which glassbeads of average particle size about 65 μm and a refractive index about1.91 were dispersed uniformly and densely substantially as a monolayer.The glass beads were then embedded in PE to about 1/3 of their diameterby pressing with nip rolls.

Onto the surface of the provisional support on which the glass beadswere exposed, aluminum was vacuum-deposited to form a vapor-coated metalmembrane of about 0.1 μm in thickness covering approximately thehemispheres of the glass beads.

Then on a release-treated, 20 μm-thick polyethylene terephthalate (PET)process film, a mixed solution of 100 parts by weight of an acrylicresin solution a 50 wt % solid solution of acrylic resin obtainedthrough copolymerization of methyl methacrylate (MMA) 20 wt %, ethylacrylate (EA) 65 wt % and 2-hydroxyethyl methacrylate (HEMA) 15 wt %, inmethyl isobutyl ketone (MIBK)/toluene (1/1)! and 14.2 parts by weight of75 wt % solid crosslinking agent derived from hexamethylene diisocyanate(HMDI) 1-methoxypropyl acetate-2/xylene (1/1) solution! was applied anddried to form an about 40 μm-thick reinforcing layer.

Further onto this reinforcing layer, a mixed solution obtained by mixing100 parts by weight of an acrylic resin solution different from theabove a 50 wt % solid solution of acrylic resin obtained throughcopolymerization of MMA 40 wt %, EA 55 wt % and HEMA 5 wt % inMIBK/toluene (1/1)! and 30 parts by weight of titanium dioxide, andfurther mixing the resultant mixed solution with 10 parts by weight ofan acrylic multistage polymerization type internal crosslinking resinsolution a 20 wt % solid solution in MIBK of MMA/butyl acrylate(BA)/styrene (ST)copolymer! and 13 parts by weight of a 15 wt % solidsolution in MIBK of cellulose acetate butyrate (CAB) was applied anddried to form an about 80 μm-thick binder layer. Thus a reinforcinglayer/binder layer laminated support layer was formed.

Next, on the metallized glass beads on the previously preparedprovisional support, the support layer was superposed with its binderlayer coming into contact with the glass beads, together heated andpressed so that the glass beads were embedded in the binder layer toabout 1/3 of their diameter, followed by 14 days' aging at 35° C. tosubstantially complete crosslinking of the reinforcing layer. Theprovisional support was then torn off from the provisionalsupport/support layer laminate, and onto the support layer on which theglass beads are exposed, a solution of UV luminescent resin compositioncomposed of 100 parts by weight of an acrylic resin solution about 50 wt% solid! "Nissetsu KP-1538S" Nippon Carbide Industries, Inc.!, 10 partsby weight of a chelate type crosslinking agent (about 6.5 wt % solid)"Nissetsu CK-401", Nippon Carbide Industries, Inc.! and 92 parts byweight of green light-emitting inorganic fluorescent agent "A-160",Nemoto Tokushu Kagaku K.K.! was printed with a pattern as illustrated inFIG. 1, using an 80-mesh silk screen, to form a UV luminescent layer(bonds) of about 100 μm in dry thickness.

On the resultant UV luminescent layer on the support layer, a 75μm-thick acrylic film "Acryprene", Mitsubishi Rayon K.K.! was mounted asthe cover layer, which was pressed with a 80° C. heated roll, to providean encapsulated lens-structured UV luminescent retroreflective sheeting.

In the resultant retroreflective sheeting, the UV luminescent regionoccupied about 62% and the retroreflective region, about 38%, to 100% ofthe incident-side surface area of said sheeting. The retroreflectivesheeting was excellent in both retroreflectivity and luminance as wellas visibility at the UV luminescent time as indicated in Table 1, andfully satisfied the purpose of the present invention.

Example 2

Example 1 was repeated except that the composition of the UV luminescentresin composition solution was changed to the one formed by blending,per 100 parts by weight of the acrylic resin solution, 8 parts by weightof the chelate type crosslinking agent and 100 parts by weight of thegreen light-emitting inorganic fluorescent agent; the screen-printedpattern was changed to a reticulated pattern of about 2 mm in line widthas illustrated as 10 in FIG. 4; and further a dotted pattern UVfluorescent layer as indicated as 5 in FIG. 4 (dry thickness: about 50μm) was printed on the surface of the cover layer using the UVluminescent resin composition solution of identical composition, with a120 mesh silk screen, and the layers were superposed in the manner thatthe UV luminescent layer of the support layer faced the UV luminescentlayer on the cover layer. Upon subsequently heating and press-adheringthem in the manner similar to Example 1, an encapsulated lens-structuredUV luminescent retroreflective sheeting was obtained.

In the resulting retroreflective sheeting the UV luminescent regionoccupied about 62% and the retroreflective region, about 38%, to 100% ofthe incident-side surface area of said sheeting. The retroreflectivesheeting was excellent in both retroreflectivity and luminance as wellas visibility at the UV luminescent time as indicated in Table 1, andfully satisfied the purpose of the present invention.

Example 3

On an about 75 μm-thick PET process film, a mixed solution composed of100 parts by weight of an acrylic resin solution a 43 wt % solidsolution of EA/MMA copolymer in MIBK/toluene (1/1), "ST-100", TokushuShikiryo K.K.! and 15 parts by weight of a chelate-type crosslinkingagent, "Nissetsu CK-401", was applied and dried to form an about 50μm-thick cover layer.

On the so obtained cover layer, a solution of a UV luminescent resincomposition composed of 100 parts by weight of an acrylic resinsolution, "Nissetsu KP-1538S", 8 parts by weight of a chelate-typecrosslinking agent, "Nissetsu CK-401", and 100 parts by weight of thesame green light-emitting inorganic fluorescent agent to that which wasused in Example 1, was printed with a 150-mesh silk screen in the mannerthat the area of the resultant UV luminescent layer should be about 55%to 100% of the cover layer area, to form a UV luminescent layer of about30 μm in dry thickness.

Next, on the resultant UV luminescent layer of the cover layer, a mixedsolution containing 100 parts by weight of an acrylic resin solution"ST-100" and 12 parts by weight of the same isocyanate crosslinkingagent to that used in Example 1 was applied and dried to provide anabout 30 μm-thick binder layer. On said binder layer glass beads of anaverage particle diameter about 68 μm and refractive index about 2.20were uniformly and densely dispersed as a monolayer, which were pressedwith nip rolls and embedded in the binder layer to about 1/2 of theirdiameter. A mixed solution of 100 parts by weight of the acrylic resinsolution "ST-100" and 5 parts by weight of the chelate-type crosslinkingagent was further applied thereon and dried, to provide an about 30μm-thick focusing layer covering approximately the hemispheres of theglass beads which were exposed on the binder layer, along their curvedsurfaces. Subsequently aluminum was vacuum-deposited on the so formedfocusing layer as an about 0.1 μm-thick vapor-coated metal membrane.Thereafter the process film was peeled off, and a sealed lens-type UVluminescent retroreflective sheeting was obtained.

In the so obtained retroreflective sheeting, the UV luminescent regionoccupied about 55% and the retroreflective region, about 45%, to 100% ofthe incident-side surface area of said sheeting. The retroreflectivesheeting furthermore was excellent in both retroreflectivity andluminance as well as visibility at the UV luminescent time as indicatedin Table 1, and fully satisfied the purpose of the present invention.

Example 4

Example 1 was repeated except that 92 parts by weight of the greenlight-emitting inorganic fluorescent agent was replaced by 95 parts byweight of a red light-emitting inorganic fluorescent agent "A-120",Nemoto Tokushu Kagaku K.K.!. Thus an encapsulated lens-type UVluminescent retroreflective sheeting was obtained.

The resulting retroreflective sheeting was excellent in bothretroreflectivity and luminance as well as visibility at the UVluminescent time, and fully satisfied the purpose of the presentinvention.

Example 5

Example 1 was repeated except that 92 parts by weight of the greenlight-emitting inorganic fluorescent agent was replaced by 92 parts byweight of a blue light-emitting inorganic fluorescent agent "A-180",Nemoto Tokushu Kagaku K.K.!. Thus an encapsulated lens-type UVluminescent retroreflective sheeting was obtained.

The resulting retroreflective sheeting was excellent in bothretroreflectivity and luminance as well as visibility at the UVluminescent time, and fully satisfied the purpose of the presentinvention.

Comparative Example 1

Example 1 was repeated except that 92 parts by weight of the greenlight-emitting inorganic fluorescent agent was replaced by 300 parts byweight of a light-storing pigment "G-500", Nemoto Tokushu Kagaku K.K.!.Thus an encapsulated lens-type UV luminescent retroreflective sheetingwas obtained.

The resulting retroreflective sheeting was short of satisfying thepurpose of the present invention, in both luminance and visibility atthe UV luminescent time, as indicated in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    UV Luminescent                                                                              Retroreflective                                                                              UV Luminance                                     Region        Region Retroreflectivity                                                                     (cd/m.sup.2)                                                                          Visibility                               (%)           (%)    (cd/1x · m.sup.2)                                                            A   B   Evaluation                               __________________________________________________________________________    Example 1                                                                           62      38     205     282 175 5                                        Example 2                                                                           62      38     203     282 175 5                                        Example 3                                                                           55      45     85      281 155 5                                        Example 4                                                                           62      38     210     82  51  5                                        Example 5                                                                           62      38     208     40  25  4                                        Comparative                                                                         62      38     208     0.134                                                                             0.083                                                                             2                                        Example 1                                                                     __________________________________________________________________________

Industrial Utilizability

The UV luminescent retroreflective sheeting of the present inventionprovides, by retroreflection of light, excellent visibility to personswho are in the direction of the light source at night and canconcurrently provide by the UV luminescence excellent visibility tothose who are in the directions other than that of the light source.

Thus, the UV luminescent retroreflective sheeting of the presentinvention can be widely utilized for markings such as road signs,construction signs, etc.; number plates on vehicles such as automobilesand motorcycles; safety goods such as safety cloths and survivalequipment; and marking materials for signboards, vehicles, etc.

We claim:
 1. Ultraviolet luminescent retroreflective sheeting comprising a retroreflective region having retroreflective elements and an ultraviolet luminescent region which emits light under ultraviolet radiation;wherein the retroreflective region comprisesan encapsulated lens retroreflective region comprising a support layer, a substantial monolayer of transparent microspheres partially embedded in one surface of the support layer, a light reflective layer coating on the portion of the transparent microspheres which are embedded in the one surface of the support layer, a transparent surface protective film facing in spaced relationship to the one surface of the support layer, and a series of bonding lines bonding the protective film to the one surface of the support layer to thereby form a plurality of sealed, small compartment cells, each of the sealed cells containing therein a part of the substantial monolayer of transparent microspheres, the non-embedded portions of which are exposed to the atmosphere within the sealed cell, or said retroreflective region comprisesan encapsulated cube-corner retroreflective region comprising a support layer; a light-transmitting cover layer spaced apart from the support layer; a layer of cube-corner retroreflective elements disposed on one surface of the cover layer facing the support layer, a series of bonding lines bonding the surface layer to the layer of cube-corner retroreflective elements and forming a plurality of sealed, small compartment cells, each of the sealed cells containing therein cube-corner retroreflective elements which are exposed to the atmosphere within the sealed cell, and wherein the bonding lines comprise a fluorescent agent which emits light under ultraviolet radiation and a resin, wherein said bonding lines form at least a portion of the ultraviolet region, and, wherein when the ultraviolet luminescent region is illuminated with a fluorescent lamp which emits near-ultraviolet rays of main wavelength around 360 nm at a light-receiving intensity of 0.8 mW/cm², the luminance is at least 10 cd/m².
 2. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein the fluorescent agent comprises inorganic fluorescent agent.
 3. The ultraviolet luminescent retroreflective sheeting according to claim 2, wherein the inorganic fluorescent agent is at least one member selected from the group consisting of red light-emitting inorganic fluorescent agent, green light-emitting inorganic fluorescent agent and blue light-emitting inorganic fluorescent agent.
 4. The ultraviolet luminescent retroreflective sheeting according to claim 2, wherein the inorganic fluorescent agent has a particle size distribution such that at least 80% by weight of the particles have a size not greater than 25 μm.
 5. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein the fluorescent agent emits light under irradiation of ultraviolet rays having a wavelength within the range of 250-400 nm.
 6. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein the ultraviolet luminescent region contains 10-600 parts by weight of said fluorescent agent, per 100 parts by weight of the resin component.
 7. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein the resin component comprises at least one resin selected from the group consisting of acrylic resins, urethane resins, polyester resins, vinyl chloride resins and fluorine-containing resins.
 8. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein the luminance of the ultraviolet luminescent region is at least 20 cd/m².
 9. The ultraviolet luminescent retroreflective sheeting according to claim 3, wherein the inorganic fluorescent agent comprises at least one red light-emitting agent selected from the group consisting of Y₂ O₃ :Eu, Y(P,V)O₄ :Eu, Y₂ O₂ S:Eu, 0.5MgF₂.3.5MgO.GeO₂ :Mn, YVO₄ :Eu and (Y,Gd)BO₃ :Eu.
 10. The ultraviolet luminescent retroreflective sheeting according to claim 3, wherein the inorganic fluorescent agent comprises at least one green light-emitting agent selected from the group consisting of Zn₂ GeO₄ :Mn, ZnO:Zn, ZnS:Cu, ZnS:(Cu, Al), (Zn,Cd)S:(Cu,Al), ZnS:(Cu,Au,Al), Zn₂ SiO₄ :Mn, ZnS:(Cu,Ag), (Zn,Cd)S:Cu, Gd₂ O₂ S:Tb, La₂ O₂ S:Tb, Y₂, SiO₅ : (Ce,Tb), CeMgAl₁₁ O₁₉ :Tb, ZnS: (Cu,Co), LaOBr: (Tb,Tm), La₂ O₂ S:Tb and BaMg₂ Al₁₆ O₂₇ : (Eu,Mu).
 11. The ultraviolet luminescent retroreflective sheeting according to claim 3, wherein the inorganic fluorescent agent comprises at least one blue light-emitting agent selected from the group consisting of Sr₅ (PO₄)₃ Cl:Eu, BaMg₂ Al₁₆ O₂₇ :Eu, BaMgAl₁₀ O₁₇ :Eu, ZnS:Ag, CaWO₄, Y₂ SiO₅ :Ce, ZnS: (Ag,Ga,Cl), Sr₂ P₂ O₇ :Eu, CaS:Bi and CaSrS:Bi.
 12. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein said retroreflective region comprises said encapsulated lens retroreflective region.
 13. The ultraviolet luminescent retroreflective sheeting according to claim 12, which further comprises an ultraviolet luminescent region on the support layer-facing surface of the light-transmitting cover layer or on the microspherical lens-embedding surface of the support layer.
 14. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein said bonding lines are formed by printing.
 15. The ultraviolet luminescent retroreflective sheeting according to claim 12, wherein, with respect to 100% of the incident side surface area of the sheeting, the areal ratio of the retroreflective region is within a range of 20-70%, the areal ratio of the ultraviolet luminescent region is within a range of 30-80%, and the sum of the areal ratios is 100%.
 16. The ultraviolet luminescent retroreflective sheeting according to claim 1, wherein the retroreflective region comprises said encapsulated cube-corner retroreflective region.
 17. The ultraviolet luminescent retroreflective sheeting according to claim 16, wherein, with respect to 100% of the incident side surface area of the sheeting, the areal ratio of the retroreflective region is within a range of 15-80%, the areal ratio of the ultraviolet luminescent region is within a range of 20-85%, and the sum of the areal ratios is 100%.
 18. A display device comprising ultraviolet luminescent retroreflective sheeting according to claim 1, in combination with an ultraviolet radiation means for radiating ultraviolet rays in the direction of said sheeting.
 19. The display device according to claim 18, wherein said ultraviolet luminescent retroreflective sheeting forms a display portion comprising one or more of characters, figures or signs.
 20. The display device according to claim 19, which further comprises a background portion for said display portion, wherein the background portion comprises retroreflective sheeting having a color different from the color of the display portion.
 21. The display device according to claim 19, which further comprises a background portion for said display portion, wherein the background portion comprises ultraviolet luminescent retroreflective sheeting having a different color tone from the color tone of the display portion.
 22. The display device according to claim 19 wherein the sheeting and the ultraviolet radiation means are integrally combined.
 23. The display device according to claim 20 wherein the sheeting and the ultraviolet means are installed at a distance one from the other.
 24. Ultraviolet luminescent retroreflective sheeting comprising a retroreflective portion and an ultraviolet luminescent portion adjacent to but not substantially overlapping with the retroreflective portion,wherein said retroreflective portion comprises retroreflective elements encapsulated within sealed cells, said sealed cells being formed by a support layer and a light transparent cover layer and bond lines connecting the support layer to the transparent cover layer; and further wherein, said bond lines comprise particles of fluorescent agent which emits light when irradiated by ultraviolet radiation, said particles being dispersed in a resin component, whereby said bond lines form said adjacent but non-overlapping ultraviolet luminescent portion; wherein when the ultraviolet luminescent region is illuminated with a fluorescent lamp which emits near-ultraviolet rays of main wavelength around 360 nm at a light-receiving intensity of 0.8 mW/cm², the luminance is at least 10 cd/m². 